Foam articles, such as trays, egg cartons and the like have been formed from continuous web stock, heated to a forming temperature and formed or molded by forming molds movable toward and from each other, and have been trimmed along the sides and leading and trailing edges of the article after forming, to separate the article from the web.
When the articles are so formed, they are subjected to the deformation stresses of the heated web still in the oven as soon as the molds open. This normally takes the form of a bowed or deformed shape of the trailing edge of the article. In order to overcome this deformation stress, the articles must remain in the molds until they are cool enough to withstand this stress without deforming. This then determines the speed at which an article can be made when all other factors in the forming system are equal.
To avoid deformation of the article at higher speeds, the article has been peripherally cut from the web to define the margin of the article, and spaced retention tabs have been used to retain the article to the web.
These tabs must then be cut or broken off to free the article from the web, leaving unsightly edges which many times are trimmed or smoothed by a separate trimming operation. The article frequently prematurely separates from the web either in the forming station or between the forming station and a subsequent trimming station for the tabs. In addition, this method has proven to be so troublesome in keeping the dies cutting that it is not considered a viable production operation. One additional fault is the limitation of only one row of articles which can be successfully formed and trimmed.
By the present invention, I avoid the deformation of the article by the stress of the web still in the oven when the molds open by heat-trimming the leading and trailing ends of the web by melting or vaporizing the web, and terminating the trimming operation by the cooled molds as they form and pressurize the edges of the article, to define the leading and trailing margins of the web. The article is then retained to the web along its sides and is advanced to a trimming station, and trimmed from the web by shearing the straight or regular sides of the article from the web.
An advantage of the present invention is that foam articles such as meat trays, egg cartons and food carry-out containers may be formed at much higher speeds without deformation of the article.
Another advantage is the superior trim accuracy of the articles formed and trimmed, and the front and rear will be exactly alike due to the fact that the mold determines the trim line.
Still another advantage is that the same side trim tools may be used for different products.
A further advantage of the invention is that the difficulty in aligning articles in the trim press for final trimming is avoided by heat-trimming the front and rear of the articles during forming and then trimming the sides of the articles and separating the articles from the web in the trim press by straight trim dies.
Other objects, features and advantages of the invention will be readily apparent from the following description of a preferred embodiment thereof, taken in conjunction with the accompanying drawings, although variations and modifications may be effected without departing from the spirit and scope of the novel concepts of the disclosure.